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Improper Encoding or Escaping of Output

CVE-2026-40021

Medium
6.3/10

Summary

Apache Log4net's XmlLayout "https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list" and XmlLayoutSchemaLog4J "https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list", in versions prior to 3.3.0, fail to sanitize characters forbidden by the XML 1.0 specification "https://www.w3.org/TR/xml/#charsets" in MDC property keys and values, as well as the identity field that may carry attacker-influenced data. This causes an exception during serialization and the silent loss of the affected log event. An attacker who can influence any of these fields can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity. Users are advised to upgrade to Apache Log4net 3.3.0, which fixes this issue.

  • LOW
  • NETWORK
  • LOW
  • UNCHANGED
  • NONE
  • NONE
  • NONE
  • NONE

CWE-116 - Improper Encoding or Escaping of Output

The software prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.

References

Advisory Timeline

  • Published